DOVER — The murder of University of New Hampshire student Elizabeth Marriott occurred during a sexual encounter, Foster's Daily Democrat has learned.

However, Foster's has been unable to confirm whether the sexual encounter was voluntary or involuntary.

Marriott, a 19-year-old UNH sophomore, disappeared on Tuesday, Oct. 9, and is now believed to be dead.

Seth Mazzaglia, a 29-year-old Dover resident, has been charged with second-degree murder in connection with Marriott's death.

Although Marriott's body has not been recovered, prosecutors say they have gathered “credible” evidence indicating Mazzaglia suffocated or strangled Marriott inside his apartment on Mill Street the night she went missing.

That night, Marriott was planning to see a female friend after leaving campus in Durham at about 9 p.m., according to Uncle Anthony Hanna. Hanna said the woman lives in an apartment on Mill Street with her boyfriend, and that she became acquainted with Marriott while they were working together at a local Target.

Marriott failed to show up for work the following morning at Target in Greenland, and was also absent from class on Thursday, Oct. 11, prompting a widespread search for the missing teenager. The attorney general's office announced Marriott's death Saturday, and Mazzaglia was arraigned on the murder charge in court Monday.

However, few details of the police investigation have been released, and documents relating to the case remain under seal at Dover District Court. Foster's Daily Democrat has petitioned the court to release police affidavits and other investigatory materials pertaining to the case to the public.

In the absence of an explanation for the death, those who knew Marriott and her suspected killer have been puzzled by the crime.

Friends and family have described Marriott as a fun-loving, trusting young woman with a wide circle of friends who was active in chorus and a prom queen in high school. She loved animals, volunteered at the New England Aquarium and helped put herself through school by working at Target.

Friends remember Mazzaglia, an aspiring actor and 2006 UNH theater graduate, as a “nice guy” who was enthusiastic about martial arts. Mazzaglia holds a black belt in karate, and has appeared in more than a dozen local theater productions.

Mazzaglia operated a number of online accounts, including a profile on the dating website OKCupid.com under the username “DarkKaiser.” Mazzaglia does not drink or take drugs, according to his page, which lists hobbies such as “gaming” and “watching movies.”

“I can be a little bit of a geek and forget how to hold a conversation if you are a woman I'm attracted to,” a statement on the page reads. “I can also be very sophisticated and articulate.”

The same user name, DarkKaiser, was used by a 29-year-old Dover, N.H., man on the website FetLife.com, an online meeting place for bondage and fetish enthusiasts. The profile indicates the user is interested in a “lifetime relationship, a play partner, princess by day, slut by night, a sub.”

At his arraignment Monday, Mazzaglia entered no plea, and was ordered held without bail in the Strafford County House of Corrections.

Explaining the second-degree murder charge, Judge Stephen Morrison said Mazzaglia is alleged to have “recklessly caused the death of Elizabeth Marriott under circumstances manifesting in extreme indifference to the value of human life...”

Marriott's body has not been recovered, and police are concentrating their search for her remains off the coast of Peirce Island in Portsmouth this week.

U.S. Coast Guard and Marine Patrol boats could be seen from shore much of the day Tuesday, and officials pulled a boot out of the water at approximately 12:30 p.m., though its relation to the case is unknown.

“Today there were as many as four vessels on the water and they employed a State Police cadaver K9 as well,” Assistant Attorney General Jane Young said.

Police have also been deploying sonar equipment an underwater camera, Young said. They have yet to set an end date for the search in the Piscataqua River.

“When we met with Marine Patrol (on Monday), the primary area they were looking at, they said they had several more days before they exhausted that area,” she said. She added authorities have also reached out to Massachusetts and Maine officials for surveillance of their shores, in case Marriott's body turns up there.

“It's almost as if we have sort of two investigations going on,” she said. “There's the recovery going on, on the water, and then Dover is leading the homicide investigation. They, too, are working tirelessly to gather as much information as they can, to make sure that the appropriate charges are brought against the appropriate person or persons.”

Young said she could not comment on additional suspects in the case, or reports that Marriott was planning to visit a female friend on the night of Tuesday, Oct. 9.

“The police continue to examine evidence gathered to date,” she said. “They continue to talk to numerous individuals, and we will continue, again, to make sure we have all of the information,” she said. “And if additional charges against additional people are warranted, they will be brought … We have to see where the evidence takes us.”

Young also declined to comment on confirmed reports by Foster's of Marriott's death being tied to a sexual encounter at the Mill Street apartment.

“I'm not saying if any information has come (from Mazzaglia),” she said. “What I've said is based on the rules of professional conduct, we can make no comment on any case — if somebody has or has not provided a statement.”